Contact Terms Research Articles

Chiral nuclear thermodynamics

We calculate the equation of state of nuclear matter for arbitrary isospin-asymmetry up to three loop order in the free energy density in the framework of in-medium chiral perturbation theory. In our approach 1π- and 2π-exchange dynamics with the inclusion of the Δ-isobar excitation as an explicit degree of freedom, corresponding to the long- and intermediate-range correlations, are treated explicitly. Few contact terms fixed to reproduce selected known properties of nuclear matter encode the short-distance physics. Two-body as well as three-body forces are systematically included. We find a critical temperature of about 15 MeV for symmetric nuclear matter. We investigate the dependence of the liquid–gas first-order phase transition on isospin-asymmetry. In the same chiral framework we calculate the chiral condensate of isospin-symmetric nuclear matter at finite temperatures. The contribution of the Δ-isobar excitation is essential for stabilizing the condensate. As a result, we find no indication of a chiral phase transition for densities ρ≲2ρ0 and at temperatures T≲100 MeV.

Efficient scrambling-free synthesis of heteroleptic terbium triple-decker (porphyrinato)(crown-phthalocyaninates)

New heteroleptic triple-decker terbium complexes of general structure [Br(4)TPP]Tb[(15C5)(4)Pc]Tb[Br(4)TPP] (Tb-TD) and [Br(4)TPP]Tb[(15C5)(4)Pc]Tb[(15C5)(4)Pc] (Tb-TD*) (Br(4)TPP = tetrakis-meso-(4-bromophenyl)-porphyrin, (15C5)(4)Pc = tetra-(15-crown-5)-phthalocyanine) are synthesized with 48% and 57% yields, respectively. The triple-decker complexes were prepared by interaction of generated in situ terbium monoporphyrinate [Br(4)TPP]Tb(acac) and corresponding double-decker precursors. The heteroleptic double-decker precursor [Br(4)TPP]Tb[(15C5)(4)Pc] was prepared for the first time in a two step one-pot synthesis. No ligand scrambling was observed in the synthesis of Tb-TD, while 4% scrambling was determined in the case of Tb-TD*. High yields of target triple-decker complexes were achieved despite the presence of electron-donating crown-ether fragments with low thermal stability at the phthalocyanine deck. Analysis of lanthanide-induced paramagnetic shifts of protons of Tb-TD together with data of previously reported La, Pr, Nd and Eu analogues allowed precise separation of contributions of contact and dipolar lanthanide terms as well as verification of isostructurality of complexes within the series.

Entropy, contact interaction with horizon, and dark energy

We present some arguments suggesting that the mismatch between Bekenstein- Hawking entropy and the entropy of entanglement for vector fields is due to the same gauge configurations which saturate the contact term in topological susceptibility in QCD. In both cases the extra term with a "wrong sign" is due to distinct topological sectors in gauge theories. This extra term has non-dispersive nature, can not be restored from conventional spectral function through dispersion relations, and can not be associated with any physical propagating degrees of freedom. We make few comments on some profound consequences of our findings. In particular, we speculate that the source of the observed dark energy may also be related to the same type of gauge configurations which are responsible for the mismatch between black hole entropy and the entropy of entanglement in the presence of causal horizon.

Fluctuations of the number of participants and binary collisions inAAinteractions at fixed centrality in the Glauber approach

In the framework of the classical Glauber approach, the analytical expressions for the variance of the number of wounded nucleons and binary collisions in $AA$ interactions at a given centrality are presented. Along with the optical approximation term, they contain additional contact terms arising only in the case of nucleus-nucleus collisions. The magnitude of the additional contributions, e.g., for PbPb collisions at Super Proton Synchrotron (SPS) energies, is larger than the contribution of the optical approximation at some values of the impact parameter. The sum of the additional contributions is in good agreement with the results of independent Monte Carlo simulations of this process. Due to these additional terms, the variance of the total number of participants for peripheral PbPb collisions and the variance of the number of collisions at all values of the impact parameter exceed several multiples of the Poisson variances. The correlator between the numbers of participants in colliding nuclei at fixed centrality is also analytically calculated.

1hJFHcoupling in 2‐fluorophenol revisited: Is intramolecular hydrogen bond responsible for this long‐range coupling?

The present study shows that a hydrogen bond between the OH group and the fluorine atom is not involved in the (1h)J(FH) spin-spin coupling transmission either for 4-bromo-2-fluorophenol or 2-fluorophenol. In fact, according to a quantum theory of atoms in molecules analysis, no bond critical point is found between O-H and F moieties. The nature of the transmission mechanism of the Fermi contact term of the (1h)J(FH) spin-spin coupling is studied by analyzing canonical molecular orbitals (see J. Phys. Chem. A 2010, 114, 1044), and it is observed that virtual orbitals play only a quite minor role in its transmission. This is typical of a Fermi contact term transmitted mainly through exchange interactions owing to the overlap of proximate electronic clouds; therefore, it is suggested to identify them as (nTS)J(FH) coupling where n stands for the number of formal bonds separating the coupling nuclei. In the cases studied in this work is n = 4. Results presented in this work could provide an interesting rationalization for different experimental signs known in the current literature for proximate J(FH) couplings.

Chiral quark dynamics and topological charge: The role of the Ramond-RamondU(1)gauge field in holographic QCD

The Witten-Sakai-Sugimoto construction of holographic QCD in terms of D4 color branes and D8 flavor branes in type IIA string theory is used to investigate the role of topological charge in the chiral dynamics of quarks in QCD. The QCD theta term arises from a compactified 5-dimensional Chern-Simons term on the D4 branes. This term couples the QCD topological charge to the Ramond-Ramond $U(1)$ gauge field of IIA string theory. The nonzero topological susceptibility of pure-glue QCD can be attributed to the presence of D6 branes, which constitute magnetic sources of the RR gauge field. The topological charge of QCD is required, by an anomaly inflow argument, to coincide in space-time with the intersection of the D6 branes and the D4 color branes. This clarifies the relation between D6 branes and the coherent, codimension-one topological charge membranes observed in QCD Monte Carlo calculations. Using open-string/closed-string duality, we interpret a quark loop (represented by a D4-D8 open string loop) in terms of closed-string exchange between color and flavor branes. The role of the RR gauge field in quark-antiquark annihilation processes is discussed. RR exchange in the s-channel generates a 4-quark contact term which produces an $\eta'$ mass insertion and provides an explanation for the observed spin-parity structure of the OZI rule. The $(\log {\rm Det\;U})^2$ form of the $U(1)$ anomaly emerges naturally. RR exchange in the t-channel of the $q\overline{q}$ scattering amplitude produces a Nambu-Jona Lasinio interaction which may provide a mechanism for spontaneous breaking of $SU(N_f)\times SU(N_f)$.

Gauge invariant two-photon exchange contributions in [formula omitted

The gauge invariant two-photon exchange (TPE) contributions in e−π+→e−π+ are discussed at hadronic level. The contact term is added to keep the full amplitude gauge invariant by two methods: one is to multiply form factors with the amplitude for point-like particles and another is to construct a gauge invariant Lagrangian. The practical calculations show the TPE contributions by these two methods are almost the same, while the later method is favored when extending the discussion to processes including two charged finite-size particles like ep→enπ+.

S-duality of S-matrix

Recently, it has been observed that the kinematic factor of the disk-level S-matrix element of two RR two-forms and the disk-level S-matrix element of two B-fields on the world volume of D$_3$-brane are compatible with the standard rules of S-duality. Inspired by this observation, we speculate that the S-matrix elements on the world volume of D$_3$-brane are invariant under the $SL(2,Z)$ transformation. Compatibility with S-duality requires the S-matrix elements on the world volume of D$_1$-brane and D$_5$-brane to be extended to the $SL(2,Z)$-covariant form. In particular, this implies the S-matrix elements on the world volume of F$_1$-string and NS$_5$-brane at strong coupling to be related by S-duality to the disk-level S-matrix elements of D$_1$-string and D$_5$-brane, respectively. %The S-matrix elements then dictate that both F$_1$-string and NS$_5$-brane have D$_1$-string excitations. The contact terms of these S-matrix elements at order $O(\alpha'^0)$ produce a Born-Infeld and Chern-Simons type effective action for both F$_1$-string and NS$_5$-brane. They are consistent with the $SL(2,R)$-covariant action appears in the literature.

Testing the density matrix expansion againstab initiocalculations of trapped neutron drops

Microscopic input to a universal nuclear energy density functional can be provided through the density matrix expansion (DME), which has recently been revived and improved. Several DME implementation strategies are tested for neutron drop systems in harmonic traps by comparing to Hartree-Fock (HF) and ab initio no-core full configuration (NCFC) calculations with a model interaction (Minnesota potential). The new DME with exact treatment of Hartree contributions is found to best reproduce HF results and supplementing the functional with fit Skyrme-like contact terms shows systematic improvement toward the full NCFC results.

Comments on 3d Seiberg-like dualities

We study Seiberg-like dualities in three dimensional N=2 supersymmetric theories, emphasizing Chern-Simons terms for the global symmetry group, which affect contact terms in two-point functions of global currents and are essential to the duality map. We introduce new Seiberg-like dualities for Yang-Mills-Chern-Simons theories with unitary gauge groups with arbitrary numbers of matter fields in the fundamental and antifundamental representations. These dualities are derived from Aharony duality by real mass deformations. They allow to initiate the systematic study of Seiberg-like dualities in Chern-Simons quivers. We also comment on known Seiberg-like dualities for symplectic and orthogonal gauge groups and extend the latter to the Yang-Mills case. We check our proposals by showing that the localized partition functions on the squashed S^3 match between dual descriptions.

Nuclear energy density functional from chiral two-nucleon aaand three-nucleon interactions

An improved density-matrix expansion is used to calculate the nuclear energy density functional from chiral two- and three-nucleon interactions. The two-body interaction comprises long-range one- and two-pion exchange contributions and a set of contact terms contributing up to fourth power in momenta. In addition we employ the leading-order chiral three-nucleon interaction with its parameters c E , c D and c 1,3,4 fixed in calculations of nuclear few-body systems. With this input the nuclear energy density functional is derived to first order in the two- and three-nucleon interaction. We find that the strength functions F ∇(ρ) and F so (ρ) of the surface and spin-orbit terms compare in the relevant density range reasonably with the results of phenomenological Skyrme forces. However, an improved description requires (at least) the treatment of the two-body interaction to second order. This observation is in line with the deficiencies in the nuclear matter equations of state $$\bar E(\rho )$$ that remain in the Hartree-Fock approximation with low-momentum two- and three-nucleon interactions.

Spacetime fermions in light-cone gauge superstring field theory and dimensional regularization

We consider the dimensional regularization of the light-cone gauge type II superstring field theories in the NSR formalism. In the previous work, we have calculated the tree-level amplitudes with external lines in the (NS,NS) sector using the regularization and shown that the desired results are obtained without introducing contact term interactions. In this work, we study the tree-level amplitudes with external lines in the Ramond sector. In order to deal with them, we propose a worldsheet theory to be used instead of that for the naive dimensional regularization. With the worldsheet theory, we regularize and define the tree-level amplitudes by analytic continuation. We show that the results coincide with those of the first quantized formulation.

Hyperfine structure interval of the2sstate of hydrogenlike atoms and a constraint on a pseudovector boson with mass below 1 keV/c2

A constraint on a spin-dependent interaction, induced by a pseudovector light boson, is presented. The interaction includes a Yukawa-type contribution $\ensuremath{\alpha}{}^{\ensuremath{''}}({\mathbf{s}}_{1}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathbf{s}}_{2}){e}^{\ensuremath{-}\ensuremath{\lambda}r}/r$ and a contact spin-spin term. To disentangle the long-range and contact terms we utilize experimental data on the $1s$ and $2s$ hyperfine intervals for light two-body atoms and construct a specific difference $8\ifmmode\times\else\texttimes\fi{}{E}_{\mathrm{hfs}}(2s)\ensuremath{-}{E}_{\mathrm{hfs}}(1s)$. That allows one to constrain the spin-dependent coupling constant $\ensuremath{\alpha}{}^{\ensuremath{''}}$ of an electron-nucleus Yukawa-type interaction in hydrogen, deuterium, and the helium-3 ion at the level below a part in ${10}^{16}$. The derived constraint is related to the range of masses below $4 \mathrm{keV}/{c}^{2}$. The combined constraint including the contact terms is also presented.

Sequestering by global symmetries in Calabi–Yau string models

We study the possibility of realizing an effective sequestering between visible and hidden sectors in generic heterotic string models, generalizing previous work on orbifold constructions to smooth Calabi–Yau compactifications. In these theories, genuine sequestering is spoiled by interactions mixing chiral multiplets of the two sectors in the effective Kähler potential. These effective interactions however have a specific current–current-like structure and can be interpreted from an M-theory viewpoint as coming from the exchange of heavy vector multiplets. One may then attempt to inhibit the emergence of generic soft scalar masses in the visible sector by postulating a suitable global symmetry in the dynamics of the hidden sector. This mechanism is however not straightforward to implement, because the structure of the effective contact terms and the possible global symmetries is a priori model-dependent. To assess whether there is any robust and generic option, we study the full dependence of the Kähler potential on the moduli and the matter fields. This is well known for orbifold models, where it always leads to a symmetric scalar manifold, but much less understood for Calabi–Yau models, where it generically leads to a non-symmetric scalar manifold. We then examine the possibility of an effective sequestering by global symmetries, and argue that whereas for orbifold models this can be put at work rather naturally, for Calabi–Yau models it can only be implemented in rather peculiar circumstances.

Quantum-Chemical Simulation of 1H NMR Spectra. 2. Comparison of DFT-Based Procedures for Computing Proton–Proton Coupling Constants in Organic Molecules

The performance of 250 different computational protocols (combinations of density functionals, basis sets and methods) was assessed on a set of 165 well-established experimental (1)H-(1)H nuclear coupling constants (J(H-H)) from 65 molecules spanning a wide range of "chemical space". Thereby we found that, if one uses core-augmented basis sets and allows for linear scaling of the raw results, calculations of only the Fermi contact term yield more accurate predictions than calculations where all four terms that contribute to J(H-H) are evaluated. It turns out that B3LYP/6-31G(d,p)u+1s is the best (and, in addition, one of the most economical) of all tested methods, yielding predictions of J(H-H) with a root-mean-square deviation from experiment of less than 0.5 Hz for our test set. Another method that does similarly well, without the need for additional 1s basis functions, is B3LYP/cc-pVTZ, which is, however, ca. 8 times more "expensive" in terms of CPU time. A selection of the better methods was tested on a probe set comprising 61 J(H-H) values from 37 molecules. In this set we also included five molecules where conformational averaging is required. The rms deviations were better than or equal to those with the training set, which indicates that the method we recommend is generally applicable for organic molecules. We give instructions on how to carry out calculations of (1)H chemical shifts and J(H-H) most economically and provide scripts to extract the relevant information from the outputs of calculations with the Gaussian program in clearly arranged form, e.g., to feed them into programs for simulating entire (1)H NMR spectra.

Publisher’s Note: Heavy-baryon chiral perturbation theory approach to thermal neutron capture onHe3[Phys. Rev. C83, 034006 (2011)

The cross section for radiative thermal neutron capture on ${}^{3}He$ ($\He3 +n \to \He4 +\gamma$; known as the $hen$ reaction) is calculated based on heavy-baryon chiral perturbation theory. The relevant M1 operators are derived up to next-to-next-to-next-to-leading order (N${}^3$LO). The initial and final nuclear wave functions are obtained from the rigorous Faddeev-Yakubovski equations for five sets of realistic nuclear interactions. Up to N${}^3$LO, the M1 operators contain two low-energy constants, which appear as the coefficients of non-derivative two-nucleon contact terms. After determining these two constants using the experimental values of the magnetic moments of the triton and ${}^3 He$, we carry out a parameter-free calculation of the $hen$ cross section. The results are in good agreement with the data.

Heavy-baryon chiral perturbation theory approach to thermal neutron capture onHe3

The cross section for radiative thermal neutron capture on ${}^{3}\text{He}$ (${}^{3}\text{He}+n\ensuremath{\rightarrow}{}^{4}\text{He}+\ensuremath{\gamma}$; known as the $\mathit{hen}$ reaction) is calculated based on heavy-baryon chiral perturbation theory. The relevant M1 operators are derived up to next-to-next-to-next-to-leading order (N$^{3}\mathrm{L}$O). The initial and final nuclear wave functions are obtained from the rigorous Faddeev-Yakubovski equations for five sets of realistic nuclear interactions. Up to $\mathrm{N}{}^{3}$LO, the M1 operators contain two low-energy constants, which appear as the coefficients of nonderivative two-nucleon contact terms. After determining these two constants using the experimental values of the magnetic moments of the triton and ${}^{3}\text{He}$, we carry out a parameter-free calculation of the $\mathit{hen}$ cross section. The results are in good agreement with the data.

THE ETA-MESON PHOTOPRODUCTION ON PROTON

We have performed the tree-level calculations of the eta meson photoproduction on proton for photon laboratory energies between 714 and 1500 MeV. The resonances N (1535), N (1710), N (1650), N (1440) and N (1520) were assumed. The form factors were introduced in the hadron vertices to involve the structure of hadrons. The influence of various form factor recipes was investigated. In order to keep gauge invariance, the appropriate contact term was introduced. The parameters of our model (coupling constants, cutoffs) were fitted to recent experimental data of the cross sections and some polarization observables.

Chiral dynamics of the [formula omitted] and [formula omitted] resonances revisited

We analyze s-wave pion–nucleon scattering in a unitarized chiral effective Lagrangian including all dimension two contact terms. We find that both the S11(1535) and the S11(1650) are dynamically generated, but the S31(1620) is not. We further discuss the structure of these dynamically generated resonances.

Experimental, SOPPA(CCSD), and DFT Analysis of Substitutent Effects on NMR 1JCF Coupling Constants in Fluorobenzene Derivatives

Interesting insight into the electronic molecular structure changes associated with substituent effects on the Fermi contact (FC) and paramagnetic spin-orbit (PSO) terms of (1)J(CF) NMR coupling constants (SSCCs) in o-X-, m-X-, and p-X-fluorobenzenes (X = NH(2); NO(2)) is presented. The formulation of this approach is based on the influence of different conjugative and hyperconjugative interactions on a second-order property, which can be qualitatively predicted if it is known how they affect the main virtual excitations entering into that second-order property. A set of consistent approximations are introduced in order to analyze the behavior of occupied and virtual orbitals, which define some experimental trends for (1)J(CF) spin-spin coupling constants. In addition, DFT hybrid functionals were used, and a similar degree of confidence to compute the (1)J(CF) with those observed for the SOPPA(CCSD) method was obtained. The (1)J(CF) SSCCs for ezetimibe, a commercially fluorinated drug used to reduce cholesterol levels, were measured and DFT-calculated, and the qualitative approach quoted above was applied. As a byproduct, a possible method to determine experimentally a significant PSO contribution to (1)J(CF) SSCCs is discussed.